Selective firing apparatus



April 30, 1968 R. Q. FIELDS SELECTIVE FIRING APPARATUS Filed May 9, 1966 2 Sheets-Sheet 1 INVENTOR R. Q. FIELDS SELECTIVE FIRING APPARATUS April 30, 1968 2 Sheets-Sheet 2 Filed May 9, 1966 INVENTOR United States Patent 3,380,540 SELECTIVE FIRING APPARATUS Roger Q. Fields, Houston, Tex., assignor to Schlumberger Technology Corporation, Houston, Tex., a corporation of Texas Filed May 9, 1966, Ser. No. 548,450 11 Claims. (Cl. 1754.55)

This invention relates to apparatus for detonating explosives; and, more particularly, to electrical means for selectively arming shaped charges in a well-perforating tool.

The present trend in well-perforating techniques is to place only one or, at most, a very few perforations at each of carefully selected points in a well rather than indiscriminately scattering a large number of perforations along a wide interval. To place such small groups or single perforations at various selected depths, apparatus carrying a number of spaced shaped charges is lowered into a well to a particular depth where a perforation is to be placed. Then, the first of one or a group of these charges is selectively detonated. Thereafter, the apparatus is repositioned at another depth and the next charge or group of charges is fired. This procedure is repeated until all of the desired perforations have been made.

Heretofore, where such selectively positioned perforations were to be made, perforating apparatus such as that shown in Patent No. 3,246,707 to William T. Bell was employed. As shown in the Bell patent, such perforating apparatus is comprised of a series of tandemly arranged individual pressure sealed hollow charge housings, with each housing constituting a single perforating unit. One or more shaped charges and a selectively initiated detonating train are enclosed in each of the charge housings. By use of suitable arming switches as fully described in that patent, each perforating unit is rendered inoperative until the unit immediately adjacent thereto has been successfully detonated.

Although such perforating apparatus has proven to be quite successful, the current trend toward smaller tubing sizes in well bores makes is difficult, if not impractical, to employ enclosed carriers such as those. It will be appreciated, of course, that the physical dimensions of a carrier that can pass through the smaller tubing sizes will drastically limit the size of the shaped charges that can be disposed therein.

Accordingly, as is customary where a well with such small tubing is to be perforated, it is preferred to employ encapsulated shaped charges dependently secured from such supports or open, carriers as a so-called strip carrier as shown in Patent No. 3,048,101 to Maurice P. Lebourg or a wire carrier as shown in Patent No. 3,282,213 William T. Bell et al. Where such strip or wire carriers are used, it will be recognized that much larger shaped charges can be used for a given size of tubing than could possibly be used were the shaped charges enclosed within a sealed carrier.

Where such open carriers are to be used for selective perforating, a series of shaped charges are tandemly arranged on the carrier, with separate electrically responsive detonating means being provided for each charge or group of charges to be fired as a unit. By using suitable electrical switching devices, the various individual charges or groups of charges can be detonated in a controlled 'sequence after they have each been positioned at a desired depth. To prevent fragments or debris from detonating charges from falling on top of still unfired shaped charges therebelow, the lowermost charges on the carrier are always the first to be fired. By successively firing from the bottom up, loose debris cannot become wedged between unfired charges and the tubing walls to most likely stick the perforating apparatus in the well bore.

3,380,540 Patented Apr. 30, 1968 ice Although such switching devices for selectively detonating shaped charges are generally reliable and foolproof, those skilled in the art will appreciate that a malfunction of either the switching device or even of a simple electrical connection is nevertheless not at all too uncommon. Thus, should such a malfunction occur, debris from successfully detonated shaped charges will be trapped in the tubing by those shaped charges therebelow that were not detonated. Since the possibility of sticking a carrier in the well bore in this manner is not too remote, it has not been considered too practical heretofore to selectively detonate shaped charges mounted on such open carriers.

Accordingly, it is an object of the present invention to provide means for reliably disarming shaped charges on a carrier so long as other charges therebelow have not yet been detonated.

This and other objects of the present invention are obtained by disposing normally-disabled enabling or electrical switching means adjacent to a first shaped charge or its detonating means and electrically connecting the switching means to the electrically initiated detonating.

means for a second shaped charge. Thus, until the first shaped charge is detonated, the second shaped charge cannot be detonated.

The novel features of the present invention are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation together with further objects and advantages thereof, may best be understood by way of illustration and example of certain embodiments when taken in conjunction with accompanying drawings, in which:

FIG. 1 schematically illustrates a firing circuit that may be used in conjunction with the arming switches of the present invention;

FIG. 2 shows in detail one embodiment of an arming switch of the present invention that may be used in the firing circuit of FIG. 1;

FIG. 3 is a cross-sectional view take along the section line 3-3 of FIG. 2;

FIG. 4 is a view of the arming switch depicted in FIG. 2 after it has been moved to its enabling position; and

FIG. 5 shows an alternate embodiment of an arming switch in accordance with the present invention.

Turning now to FIG. 1, a schematic representation is shown of shaped charge perforating apparatus 10 employing the present invention. The apparatus 10 includes a support 11 which, for example, may be either the strip carrier shown in Patent No. 3,048,101 or the spaced wire carrier shown in Patent No. 3,282,213. The carrier 11 is dependently suspended in the usual manner from a monocable 12 which has a single inner electrical conductor 13 and an electrically conductive outer armor sheath 14 as the other electrical conductor. This monocable 12 is, of course, suitably arranged for being spooled in the usual manner from a winch (not shown) adjacent to the well bore.

A regulated and controlled voltage source 15, such as provided by a battery 16 having a potentiometer 17 across it and in series with an ammeter 18 and a control switch 19, is connected across the conductors 13 and 14 at the upper end of the monocable 12. Thus, by adjusting the potentiometer 17, it will be appreciated that the voltage potential across the conductors 13 and 14 may be varied as required.

At the upper end of the carrier 11, an enclosed housing 20 interconnects the carrier to the lower end of the monocable 12. Sealingly enclosed within this housing 20 is a conventional solenoid-actuated, stepping-type selector switch 21 that responds to sequential electrical energizations to successively connect a selected number of a plurality of longitudinally spaced shaped charges 22 mounted along the carrier 11 to the central conductor 13 of the monocable 12 so that the charges may be sequentally detonated. Although it may be desired to detonate more than one shaped charge at any given time, only one of the shaped charges 22 has been shown connected to a single switch contact for purposes of greater clarity.

To accomplish this, the selector switch 21 has a solenoid actuator mechanism 23 for porgressively advancing a rotatable switch contact 24 around a plurality of circumferentially spaced contacts 25 on a multi-contact switch wafer 26-. Although other suitable advancing mechanisms might be used, the preferred mechanism employs a pawl (not shown) actuated by the solenoid 23 that indexes a rotatable ratchet wheel (not shown) connected to the rotatable switch contact 24 one position each time the solenoid is energized. The solenoid actuator 23 is suitably arranged to hold the pawl against the ratchet wheel so the switch contact 24 will remain in the position that it has just moved into. Then, when the solenoid actuator 23 is de-energized, the pawl returns and engages the next tooth on the ratchet wheel without further movement of the rotatable switch contact 24. This solenoid actuator 23 therefore cannot advance the rotatable switch contact 24 further until the energizing voltage is first decreased so as to reposition the pawl. Thus, by successively energizing and de-energizing the solenoid actuator 23, the contact 24 is advanced one position at a time around its switch wafer 26 for each cycle of the solenoid.

The contacts 25 on the wafer 26 of the selector switch 21 are arranged to sequentially connect the shaped charges 22 in turn to the regulated voltage source for subsequent detonation as desired. Thus, although only a few shaped charges 22 have been shown on the carrier 11, it will be understood that the contacts on the switch wafer 26 are each connected as desired to one or more shaped charges.

Accordingly, when the solenoid actuator 23 is first energized, the rotatable contact 24 is shifted from its initial starting position (as depicted in FIG. 1) which has no conductor leading therefrom to the first contact 25a where it then stops. An electrical circuit is thereby established through a Zener diode 27 and the rotatable contact 24 to this first contact 25a; and, from there, through a conductor 28a, to a typical electrically initiated detonator 29a which is, in turn, coupled to a detonating cord 30a secured .to the rear of the shaped charge 22a to be fired first. A separate conductor 31a is connected from the detonator 29a to the carrier 11 to provide a return path to the monocable sheath 14.

Thus, as will subsequently be explained in greater detail, once the rotatable contact 24 has been moved to the first fixed contact 250, an electrical circuit will be established between the power source 15 and the lowermost shaped charge 22a on the carrier 11. Then, when sufficient voltage is applied to the detonator 29a, the detonator and the detonating cord 3011 will be exploded and in turn detonate the lowermost shaped charge 22a.

It will be noted from FIG. 1 that the detonating cord 30a is extended from the lowermost shaped charge 22a and disposed adjacent to an electrical switch 32a arranged in accordance with the principles of the present invention. As will subsequently be described in greater detail, this arming switch 32a is normally open so as to interrupt the electrical circuit of the detonator 29b for the next shaped charge 22b immediately thereabove in the carrier 11. Similarly, a second arming switch 32b also arranged in accordance with the principles of the present invent-ion is conencted in the same manner to the electrical detonator 290 for detonating the uppermost shaped charge 220. The second arming switch 32b is disposed immediately adjacent the detonating cord 3% employed to detonate the intermediate shaped charge 22b. Thus, irrespective of the position of the rotatable selector switch 21, the shaped charges 22!) and 220 cannot be detonated until their respective arming switches 32a and 32b are closed.

Turning now to FIG. 2, one embodiment is shown of an arming switch arranged in accordance with the present invention that might be used for the arming switches 32a and 32b shown in FIG. 1. The arming switch 40 is comprised of a tubular shell 41 of an electrical conductive material in which an electrically conductive mernber, such as a rod 42, is co-axially disposed. To support the rod 42 within the shell 41, a closure member 43 is received in one end of the shell and one end of the rod is secured thereto, as by threads 44. The opposite end of the shell 41 is also closed as by an end wall 45.

One or more annular members 46 of an electrically conductive material are disposed at space-d intervals along the free portion of the conductive central rod 42. For reasons that will subsequently be explained in greater detail, these annular members 46 are serrated, as at 47 (FIG. 3), around their circumference. A thin sleeve 48 of an electrically non-conductive material, such as one of the typical insulating plastics, is slipped over the free end of the central rod 42 as well as the annular members 46 thereon.

It will be appreciated that under the conditions typically encountered in a well bore, the fluid pressures therein can be quite substantial. Accordingly, the shell 41 and its end wall must be of sufficient strength to withstand such substantial pressures. Similarly, the closure member 43 must be fluidly sealed within the open end of the shell 41 to prevent entry of fluids therein. It also will be recognized that an electrical conductor must be connected to the conductive rod 42 and brought out of the shell 41 in some manner that will prevent entry of fluids as well as to maintain both the rod and conductor electrically insulated from the shell.

Accordingly, although a closure member could be formed from a non-conductive material such as glass, plastic, or the like, it is preferred to form the, closure member 43 from an electrically conductive but solid material. An insulated electrical conductor 49 can therefore be secured to the closure member 43 as, for example, by disposing its bared end 50 within a complementary socket formed in the outer face of the closure member. In this manner, the necessity of otherwise providing a passage through the closure member 43 for a conductor to be passed and fluidly sealed is avoided.

To fluidly seal the closure member 43 to the shell 41, sealing means, such as an O-ring 51 disposed in a complementary groove around the closure member, are provided. Moreover, to prevent pressure differentials from moving the closure member 43 further inwardly into the shell 41 where the free end of the rod 42 might contact the closed end wall 45 of the shell, the outer portion 52 of the bore in the shell 41 is enlarged so as to provide an outwardly facing shoulder 53 on which the closure member 43 is engaged. The outer enlarged bore portion 52 in the shell 41 is then filled with a suitable non-conductive material, such as an elastomeric or plastic substance 54, to minimize the entry of fluids into the enlarged bore portion.

It will be recognized that by making the closure member 43 of a rigid conductive material, it can be reliably sealed to the shell 41 by the O-ring 51. This, however, requires that suitable means he provided for electrically insulating the closure member 43 from the shell 41 without providing a leakage path between the insulation and the outer surface of the closure member through which fluids could enter the shell.

Accordingly, to insulate the closure member 43 from the shell 41, the closure member is constructed from aluminum and at least those outer surfaces contiguous with the shell (as indicated by the dotted markings 55 in FIGS. 2 and 4) are hard-anodized to a depth of at least about 0.001 to 0.002-inch. For the relatively low voltages customarily used for detonating explosives, this hardanodizing provides an excellent electrical insulating surface on the closure member 43 while still allowing efiective transmission of electricity through the body of the closure member. Thus, it will be appreciated that so long as the central rod 42 and annular members 46 do not contact the inner wall of the shell 41, the electrical conductor 49 will be in electrical contact through the closure member 43 with the rod but will be electrically isolated from the shell. By disposing the protective sleeve 48 around the annular members 46 and rod 42, a further measure of protection is afforded should there be some eccentricity or shifting of the rod within the shell 41.

As seen in FIG. 2, to employ the arming switch 40 of the present invention in the manner illustrated, for example, in FIG. 1, a portion of a detonating cord 56 is disposed adjacent to the shell 41 and, if necessary, is secured thereto, as by tape. By disposing the detonating cord 56 at least adjacent to the portion of the shell 41 in which the rod 42 is confined, it will be appreciated that upon detonation of the detonating cord the resultant detonating shock will at least partially collapse the shell.

Accordingly, :as best seen in FIG. 4, upon detonation of the detonating cord 56, the wall of the shell 41 will be driven inwardly, as at 57, against the most proximate peripheral edges 47 of the annular members 46. By providing the serrations 4'7 thereon, the sharp edges of the annular members 46 will puncture the plastic sheath 48 and become embedded at at least several points along the inner surface of the shell 41. In this manner, electrical contact will be positively established between the electrically isolated conductive rod 42 and conductor 49 to the shell 41 itself. Accordingly, by making a suitable electrical contact with the shell 41 (as by clamping or affixing a conductor thereto), the arming switch 40 will function as a simple normally-open switch that will be positively closed only by the high-order detonation of the juxtaposed detonating cord 56.

Returning now to FIG. 1, it will be seen that the arming switch 32a is operatively anranged relative to a portion of the detonating cord 30a for the lowermost shaped charge 22a so that this shaped charge must be detonated before the arming switch 320 can be closed. Thus, the intermediate shaped charge 22b cannot be detonated until the first shaped charge 22a has been detonated. Similarly, by placing the other arming switch 32b in series with the detonator 29c, the uppermost shaped charge 220 in the carrier 11 will remain inoperative until the intermediate shaped charge 22b has been detonated.

It will be appreciated, therefore, that although the rotatable contact 24 might, for example, be advanced too soon to the second contact 25b, the intermediate shaped charge 22b cannot be detonated until the lowermost shaped charge 22a has been detonated and closed the arming switch 320. Thus, there would be no possibility for debris from the intermediate shaped charge 22b to fall downwardly and become lodged between the lowermost but still unfired shaped charge 22a and the inner wall of the well bore.

Turning now to the operation of the perforating apparatus 1t), assume that the selector switch 21 is in its initial starting position as depicted in FIG. 1 and that the perforating apparatus is now in position within a well for detonating the first of the shaped charges 22a on the carrier 11. The switch 19 at the surface of the ground is first thrown to connect the power source to the perforating apparatus 10-.

It will be appreciated that with the potentiometer 17 at its extreme left-hand position (as depicted in FIG. 1), the voltage potential across the conductors 13 and 14 will be negligible. Moreover, by selecting the Zener diode 27 to have a Zener level that is greater than the voltage potential required to actuate the solenoid actuator 23, the selector switch 21 can 'be actuated before the voltage applied across the conductors 13 and 14 has reached the Zener level of the Zener 27. Furthermore, since, as already described, the actuating mechanism 23 of the selector switch 21 can not be returned until its solenoid has been de-energized, a continued application of voltage to the solenoid actuator will not index the rota-table contact 24 to another contact 25 so long as the voltage is not reduced.

Accordingly, to operate the perforating apparatus 10 with the selector switch 21 in its initial starting posi tion as depicted in FIG. 1, the control switch 19 is closed and the potentiometer 17 is advanced in the direction of arrow 33 to increase the voltage applied across the monooable 12 to a level suthcient to actuate the solenoid actuator mechanism 23 of the selector switch 21. Once the selector switch 21 has been actuated, the rotatable contact 24 is stepped from its inactive position shown in FIG. 1 to the first contact 25a on the switch wafer 26.

The shaped charge 220 connected to the contact 25a will not be immediately detonated, however, since, so long as the voltage across the conductors 13 and 14 is less than the Zener level of the Zener diode 27, current cannot flow through the Zener to the :detonator 29a. It will be recalled as well that the rotatable contact 24 cannot be fiurther advanced unless the votage has been first reduced. Thus, if desired, the potentiometer 17 can be halted in its intermediate position to delay detonation of the shaped charge 220.

Once, however, the potentiometer 17 is advanced further in the direction of the arrow 33, the voltage across the conductors 13 and 14 of the monocable 12 will subsequently reach a potential equal to the Zener level of the Zener diode 27. Then, 'by continuing to increase the voltage across the conductors 13 and 14 to a. magnitude greater than the Zener level of the Zener diode 27, the detonator 29a connected to the contact 25a of the switch wafer 26 willfinally be detonated and in turn detonate the shaped charge 22a. Detonation of the lowermost shaped charge 22a will, of course, serve to close the arming switch 3241 so as to enable the firing circuit for the intermediate shaped charge 22b. It will also be recalled that the rotatable contact 24 can not be indexed to its second position until the voltage across the solenoid actuator 23 is reduced.

Upon returning the potentiometer 17 to its initial position, the solenoid actuator 23 will be de-energized when the voltage drops to a minimum level suflicient to allow the indexing mechanism of the selector switch 21 to return to its initial position. Then, whenever the perforating apparatus 10 has been repositioned in the well bore, the potentiometer 17 is again advanced in the direction of the arrow 33 to index the rotatable contact 24 to its second operative position 25b and connect the next detonator 2% into the firing circuit. As already described, the electrical circuit for the detonator 2% was partially completed upon closure of the arming switch 32a by the detonation of the lower shaped charge 22a. Thus, by repeating the same procedure already described, the intermediate shaped charge 22b can now be detonated.

Similarly, it will be noted by virtue of the normallyopen arming switch 32b in the firing circuit of the third shaped charge 22c, this shaped charge also cannot be detonated until this arming switch 3212 has been crushed by the detonation of the intermediate shaped charge 22b. Thus, to detonate the third shaped charge 22c as well as any other charges thereabove (not shown) the same procedure must again be followed after the intermediate shaped shaped charge 22b has been detonated before this third shaped charge 220 can be detonated.

Turning now to FIG. 5, an alternate embodiment is shown of an arming switch 70 also arranged in accordance with the present invention. This arming switch 70 is in many respects similar to the arming switch 40 already described so it is believed necessary only to point out the diiferences therebetween. For this arming switch 70, the outer shell 71 is similarly formed of a conductive material. In distinction with the other arming switch 40, however, the arming switch '70 depicted in FIG. 5 is confined in an open-ended tubular shell 71. An electrically conductive rod 72 is co-axially disposed within the shell 71 and secured at one end to a closure member 73 of an electrically non-conductive material. A plurality of annular members 74 having toothed or serrated peripheral edges, as at 75, are secured around the central rod 72 and appropriately dimensioned so that upon crushing of the shell 71, they will become embedded within the inner surface of the shell. The remainder of the bore 76 through the shell 71 is filled with an electrically nonconductive material such as an elastomer 77. The bared end 78 of an electrical conductor 79 is secured to one end of the central rod 72 with the elastomeric material 77 being bonded to both the inner surface of the shell 71 and outer surface of the rod and conductor to complete a fluid seal.

It will be appreciated, of course, that the arming switches 40 and 70 already described can be used with equal success in the circuit arrangement depicted in FIG. 1. Moreover, those skilled in the art will appreciate that these arming switches 40 and 70 may be used with equal advantage in other circuit arrangements suitable for selected detonation of two or more individual charges or groups of shaped charges. As a partial example of such circuit arrangements, attention is directed to those described in the aforementioned Bell patent.

Accordingly, it will be recognized that the present invention has provided new and improved enabling means for positively preventing detonation of a second explosive means so long as a first explosive means has not been detonated previous thereto. By employing the arming switches 40 and 70 of the present invention as described, it is essential for a first explosive to be detonated at highorder before a second explosive detonated by electrical means including one or these arming switches can be enable. Thus, whether the electrical source is inadvertently or deliberately connected to the detonating means for the second explosive, this second detonating means will be disabled and cannot be enabled until the first explosive is detonated.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. Well perforating apparatus comprising: explosive perforating means; means responsive to an electrical signal for detonating said explosive perforating means; normallyopen switch means including a tubular first electrical conductor and a second electrical conductor disposed in said tubular conductor and normally spaced therefrom, one of said electrical conductors being connected to an electrical source and the other of said electrical conductors being connected to said detonating means; and explosive means adjacent to said tubular conductor and selectively detonatable for collapsing said tubular conductor into electrical contact with said second electrical conductor.

2. The apparatus of claim 1 further including electrical insulating means between said electrical conductors and means on one of said electrical conductors for penetrating said electrical insulating means whenever said tubu- 8 lar conductor is collapsed to establish electrical contact between said electrical conductors.

3. The apparatus of claim 1 further including means for fluidly sealing said second electrical conductor within said tubular conductor.

4. The apparatus of claim 1 further including means for fixing said second electrical conductor within said tubular conductor.

5. The apparatus of claim 4 further including means for fluidly sealing said second electrical conductor within said tubular conductor.

6. The apparatus of claim 4 further including electrical insulating means between said electrical conductors and means on one of said electrical conductors for penetrating said electrical insulating means whenever said tubular conductor is collapsed to establish electrical contact between said electrical conductors.

7. The apparatus of claim 6 further including means for fluidly sealing said second electrical conductor within said tubular conductor.

8. The apparatus of claim 7 wherein said explosive means includes second explosive perforating means and second means responsive to an electrical signal for detonating said second explosive perforating means.

9. As a subcombination, an arming switch adapted for use with well apparatus comprising: a tubular member of electrically conductive material; an electrical conductor disposed in said tubular member and normally spaced from the interior surfaces thereof; means for fluidly sealing said electrical conductor within said tubular member and means for establishing electrical contact between said conductor members upon inward collapse of said tubular member.

10. The arming switch of claim 9 further including electrical insulating means between said tubular member and said electrical conductor, said contact-establishing means including means on one of said conductor members for piercing said electrical insulating means upon inward collapse of said tubular member to establish electrical contact between said conductor members.

11. The arming switch of claim 10 wherein said piercing means includes a member on said electrical conductor having a sharpened lateral projection.

. References Cited UNITED STATES PATENTS 3,010,396 11/1961 Coleman 4.55 3,038,042 6/1962 Hall et al 2006l.08 3,077,027 2/1963 Sola et al 339276 X 3,116,689 1/1964 Sumner 1754.55 X 3,117,194 1/19-64- Stresau 20061.08 3,155,876 11/1964 Paul 200--61.08 X 3,246,707 4/1966 Bell 1754.55 X 3,327,792 6/1967 Boop 175-4.55 X

FOREIGN PATENTS 217,400 10/1958 Australia.

798,499 7/ 1958 Great Britain.

808,698 2/ 1959 Great Britain.

CHARLES E. OCONNELL, Primary Examiner.

DAVID H. BROWN, Examiner. 

9. AS A SUBCOMBINATION, AN ARMING SWITCH ADAPTED FOR USE WITH WELL APPARATUS COMPRISING: A TUBULAR MEMBER OF ELECTRICALLY CONDUCTIVE MATERIAL; AN ELECTRICAL CONDUCTOR DISPOSED IN SAID TUBULAR MEMBER AND NORMALLY SPACED FROM THE INTERIOR SURFACES THEREOF; MEANS FOR FLUIDLY SEALING SAID ELECTRICAL CONDUCTOR WITHIN SAID TUBULAR MEMBER AND MEANS FOR ESTABLISHING ELECTRICAL CONTACT BETWEEN SAID CONDUCTOR MEMBERS UPON INWARD COLLAPSE OF SAID TUBULAR MEMBER. 